Stretching of self-interacting wormlike macromolecules

Structural and elastic properties of non-charged polymers of stiffness ranging from flexible to rigid chains are computed by Monte Carlo simulations. A discrete wormlike chain (WLC) model with self-interacting units is applied to chains of intermediate lengths of interest in the AFM measurements. Variations of the persistence length and mean chain dimensions with bending stiffness are presented. The chain-end distribution functions, the Helmholtz elastic energy and the force-extension profiles of chains of variable stiffness are computed in an isometric ensemble. Occurrence of a plateau on the force-extension curves at intermediate chain stiffness is noted. Qualitative differences are found between force profiles from simulations and from the standard (ideal) WLC model. The differences can be ascribed to an inherent dissimilarity between isometric and isotensional ensembles used and, at small extensions, to the excluded-volume effects. The single-chain functions from simulations were employed to investigate the influence of bending stiffness on elasticity of networks of semiflexible chains by the three-chain model. A stark reduction of degree of elongation of a network with rising stiffness is found. Stress-strain relations show a highly non-linear behavior with the marked strain-stiffening effect.